The present invention relates to an information recording apparatus, such as an optical disc drive, that records information in a recordation medium, such as a CD-R/RW disc, and in particular, to a light intensity control apparatus that controls power of a light generated from a light source such as a semiconductor laser.
Recently, an information recording apparatus capable of recording information in a recordation medium, such as a CD-R/RW disc, is in widespread use. For example, Japanese Patent Application Publication No. 7-44885 refers to an information recording apparatus, where the first, third and fourth levels of light intensity (P1, P3, and P4) are set as optical output levels of a semiconductor laser. In addition, the remaining second intensity level (P2=P1+P4xe2x88x92P3) can be set from the three lower optical intensity levels (P1, P3, and P4) as a peak value of a recordation pulse light because the optical intensity value P3 is smaller than P1, and the following inequality is accordingly established:
P4 less than P2, P3 less than P4 less than P2
As a result, an unnecessary signal (i.e., signal higher than P2) can be avoided from being recorded in the recordation medium. Accordingly, unnecessary deterioration of the semiconductor laser can be avoided.
Further, when recording some information in an optical disc, an optical disc apparatus as an information recording apparatus generally modulates a recordation laser beam with a higher recordation power (i.e., a higher optical output level) than when reading information.
When utilizing a writable optical disc, such as a CD-R (Compact Disc Recordable) disc, having an organic colorant recordation coat on a recordation surface, the semiconductor laser light source alternately generates light beams having light power levels P1 (xe2x80x9creadxe2x80x9d intensity) and P2 (xe2x80x9cwritexe2x80x9d intensity), where P2 is an optical output light power level higher than P1. As a result, a xe2x80x9cpitxe2x80x9d is created on a portion of the recordation surface when the laser light beam is irradiated at the generated light power level P2, and a xe2x80x9cspacexe2x80x9d remains on another portion when the other portion is irradiated by the generated light power P1. Further, the P3 level, which is higher than the P2 level, is generally utilized and a recordation power wave sometimes is formed to include three different values having P1, P2, and P3 levels. The P3 level is positioned at a pit top portion so as to make a pit edge sharp.
When a rewritable and phase changeable type recordation medium, such as a CD-RW (Compact Disc Rewritable) disc, is utilized, these three optical output power levels are also used. Specifically, a portion irradiated by a laser beam on a recordation surface portion is generally made amorphous (non-crystal) when the generated light power P3 and P1 levels are repeatedly utilized at high speed. In contrast, a crystal portion is made on the recordation surface when the P2 level is maintained. These crystalline and amorphous portions can correspond to information data.
To control these several modulation intensity levels, a sampling circuit is generally utilized. When the generated light intensity levels P1 and P2 for the CD-R are utilized, the P2 level is sampled and is generally compared with a prescribed reference value. Then the laser current carried through the semiconductor laser light source is controlled based upon the result of the comparison.
Thus, the generated light power is controlled so that the P2 level can equal a prescribed reference level (i.e., target level). In addition, since the P1 level corresponds to reading power, the magnitude of laser current carried during reading generally is stored for later use.
In the above-described information recording apparatus, when the modulation speed becomes extremely high along with an increase in a recordation speed, the time period of the P2 level becomes extremely short. As a result, a high speed sampling circuit is required. However, it generally is difficult to provide such a high speed sampling circuit, or costly if provided. In addition, if a less expensive sampling circuit is utilized, the recordation light power is not precise.
An object of the present invention is to address and resolve the above and other problems and provide a new image processing apparatus. The above and other objects are achieved according to the present invention by providing a novel light intensity control apparatus including a light source driving device that drives a light source by the first and second light intensity levels, a light intensity detection device that detects intensity of a light generated from the light source, a comparison device that compares the light intensity with the first and second reference levels, and a driving current adjustment device that adjusts magnitude of a driving current that drives the light source in accordance with a result of the comparison.
In another embodiment, the light intensity detection device includes a first light intensity detection member that detects intensity of the light generated by the second light power level when an operational speed is relatively low, and a second light intensity detection member that detects an average of the intensity of the light when an operational speed is relatively high.
In yet another embodiment, a light intensity detection member selection device is provided so as to select one of the first or second light intensity detection devices based upon a selection instruction so as to select one of the detection outputs.
In yet another embodiment, the comparison device includes a reference level selection device that selects one of the first and the second reference levels in accordance with the selection instruction.
In yet another embodiment, the selection instruction indicates a digital modulation speed of the light source.
In yet another embodiment, the selection instruction controls the detection member selection device to select the first light intensity detection member and the reference level selection device to select the first reference level, correspondingly, when the digital modulation speed is relatively low.
In yet another embodiment, the selection instruction controls the detection member selection device to select the second light intensity detection member and the reference level selection device to select the second reference level when the digital modulation speed is relatively high, where the high speed is higher than the low speed.
In yet another embodiment, the light source driving device drives a light source by all of the first, second, and third light intensity levels.
In yet another embodiment, the driving current adjustment device adjusts the magnitude of the driving current so that the light source generates a light power intensity level having the second reference level based upon the result of the comparison when the light source is driven by the second light generation level.
In yet another embodiment, the driving current adjustment device adjusts the magnitude of the driving current in accordance with the performance derived from the first and second generated light levels when the light beam is generated at the third light intensity level.